Current technology involves the cooling of ceramics using air conveyed by electric blowers into the cooling sections, which especially in kilns require expensive structures, stretching for many meters: this involves high plant construction and operating costs, in addition to the extensive space requirements and high capital investment, without considering the emission into the atmosphere of hot air at about 150.degree. C. from the kiln.
There is considerable scope for improvement of this state of the art in relation to the possibility of eliminating the problems mentioned without damaging the product or impairing its quality.
From the above consideration there derives the need to solve the technical problem of identifying a new method providing a largescale reduction in the construction and operating costs of the cooling plant for ceramic products leaving the high-temperature pre-treatment chamber and/or leaving the firing chamber, or in any heated state after which cooling is required: i.e. for any type of ceramic plant to which the new method is applicable.
This method must be suitable for application both to new kilns and to those already in operation, with structural modifications in the case of the latter.
The present invention solves the above technical problem by adopting a method involving passing the hot ceramic articles through water, by immersion, and/or in jets, and/or sprayed, and/or nebulized and/or in the form of steam: the latter case is especially suitable for the areas with highest temperature, obtaining all or part of the steam required from the steam generated by water-cooling in lower-temperature zones. When very hard water is used, and in all cases concerning glazes on which calcium salts deposited by the cooling water would be noticeable, the method envisages cooling from beneath only, i.e. on the rear of the tile, without the projection of any water which might reach the upper surface which has been glazed or is destined for decoration in any way.
The plant implementing the method includes at least one booth, preferably subdivided into one or more cooling stations: with upper and lower spray nozzles spraying out water, with upper and lower packs of disks revolving at high speed and projecting water by centrifugal force, by immersion, providing steam, or mixed. The steam generated by the water cooling process is removed by fans, while excess water is recycled.
In all cases the heat may be recycled using heat exchangers. When cooling is on the underside of the tile only, in order to prevent the deposit of calcium salts on the face intended to remain in view, the system incorporates idle or power-driven sponge transversal rollers provided with water from the inside or picking up water from below, which wet the tiles from underneath the conveyor belt line.
In the case of cooling from temperatures significantly above 150.degree. C., since the tiles are to be conveyed on rollers, said rollers will be hollow and given radial holes to sprinkle the underside of the row of tiles with water supplied to the rollers themselves under a slight pressure.
In an exemplary application of the method constructed for a roller kiln already installed for production of 10,000 m.sup.2 /day of glazed and unglazed tiles, with a weight of approximately 13 kg/m.sup.2, with feed speed approximately 5 m/min., the system comprises a booth with water cooling successfully provided by means of two rows of nozzles arranged above and below the tile route, with a field of 0.5 m for each nozzle, forming a sprinkling zone 1 m in length.
The booth, in stainless steel which may be replaced by plastics in the lower-temperature zones, measuring 3 meters in length comprising a final roller conveyor of 2 meters in length, replaces the final section of the kiln with the air cooling function, which was no less than 30 meters long. The booth intake point, located less than 1 m from the firing chamber exit, receives tiles at a temperature of approximately 1100.degree. C., while their temperature on leaving the booth is about 20.degree. C.
The nozzles are supplied with well water by means of a standby tank of approximately 1 m, by means of a pump with delivery rate 31 liters/min and a 2" pipe with recycling. A fan removes 10,000 kg/day of steam from the booth, equivalent to approximately 7 kg/min (at atmospheric pressure), amounting to 28 m/min. Water consumption is thus only 10 m.sup.3 /day.
In another application of the method installed on a roller kiln with output 7,448 m.sup.2 /day of glazed and unglazed tiles, weighing approximately 13 kg/m.sup.2, with feed speed 4.2 m/min, the system comprises a water cooling booth equipped with three water pipes arranged above and below the tile route, each equipped with seven spray nozzles, supplied with water at a pressure of 5 bar.
The temperature of the tiles, which is approximately 400.degree. C. when they enter the booth, is reduced to 80.degree. C. over a distance of just one meter: in any case, the speed at which cooling occurs depends on the porosity of the tile bodies, increasing as the porosity decreases. There is a slight vacuum inside the cooling booth, in order to aid extraction of the steam which forms during cooling. The amount of non-recycled water consumed in one hour is approximately 1.6-1.7 m.sup.3, with the option of reducing this by up to one half by recycling the cooling water. The cooling cycle is synchronized with the entire production process: the amount of water used is proportional to the temperature variations and the mass for cooling.
The advantages obtained with this invention are: reduction in the area of the cooling zone by up to 95%; the possibility of recycling the steam produced; reduction of the need for monitoring to a much smaller area; cooling in a closed cycle or with minimal emissions to the outside, with the resulting advantages for the environment; the use of a fluid with cooling power approximately 6 times greater than that of air; extremely compact cooling zone; energy saving; saving on plant costs; possibility of using steam generated by the cooling process for cooling higher-temperature areas; automatic regulation of the water cooling process in relation to temperature and mass; energy recycling; the option of using the steam generated by the cooling process in spray-drying plants; greater operating flexibility; possibility of partial applications if required, and the possibility of eliminating the formation of calcium salt deposits on the tile face.